Brief high-intensity exercise in healthy men significantly increased circulating IGF-I by 13.3% (P<0.002), IGF-II by 15.7% (P<0.01), and IGFBP-3 by 23% (P<0.001) compared to baseline.
Does brief low- and high-intensity exercise increase circulating levels of the GH/IGF system in young healthy men?
Brief exercise leads to intensity-dependent increases in circulating IGF-I, IGF-II, IGFBP-3, and IGFBP-3 proteolysis in young healthy men.
We measured circulating levels of the GH insulin-like growth factor (IGF) system in response to brief exercise of different intensities. Ten males (mean age 28 +/- 5 yr) were studied on three separate occasions: once under resting conditions (control) and once each performing 10 min of low- or high-intensity exercise. Blood samples were assayed by RIA for GH, IGF-I and -II, IGF-binding protein-3 (IGFBP-3), and IGFBP-3 proteolytic activity. After 10 min of low-intensity exercise, IGF-I and IGFBP-3 had increased over preexercise baseline by 7.7 +/- 2.7% (P < 0.05) and 12.5 +/- 3.3% (P < 0.004), respectively. After 10 min of high-intensity exercise, all measured components of the IGF system were increased: IGF-I by 13.3 +/- 3.2% (P < 0.002), IGF-II by 15.7 +/- 3.1 (P < 0.01), and IGFBP-3 by 23 +/- 6% (P < 0.001). IGFBP-3 proteolytic activity also was increased (44 +/- 14% above baseline, P < 0.05). GH reached its peak 10 min after the cessation of high-intensity exercise, unlike the earlier peaks of IGF-I and II. In summary: 1) brief exercise leads to small but significant increases in circulating IGF-I, IGF-II, IGFBP-3, and IGFBP-3 proteolysis; and 2) these responses may be influenced by exercise intensity. The IGF responses seem to be unrelated to GH. Acute exercise-induced proteolysis of IGFBP-3 may contribute to anabolic effects of physical activity by increasing the bioavailability of IGF-I.
Schwarz et al. (1996) studied Healthy (n=10). Low- and high-intensity exercise vs. Resting conditions (control) was evaluated on Circulating levels of GH, IGF-I, IGF-II, IGFBP-3, and IGFBP-3 proteolytic activity. Brief high-intensity exercise in healthy men significantly increased circulating IGF-I by 13.3% (P<0.002), IGF-II by 15.7% (P<0.01), and IGFBP-3 by 23% (P<0.001) compared to baseline.